The present invention relates to a single shaft type table feed device including a movable body and an auxiliary movable body and, in particular, to a single shaft type table feed device in which the auxiliary movable body can fill a role of the part of an intermediate support, to thereby be able to enhance the critical speed of a feed screw shaft.
Conventionally, as a table feed device using a feed screw shaft, there are known various types of table feed devices. One of them is a single shaft type table feed device which is a feed screw integrally combined linear guide device obtained by combining a feed screw device with a linear guide device into an integrally united body.
In particular, a single shaft type table feed device to be improved by the invention is a single shaft type table feed device in which there are mounted not only a movable body including a screw nut portion engageable with the feed screw shaft but also an auxiliary movable body not including a screw nut portion so as to enhance the resistance of the feed screw shaft to a load applied thereto.
Recently, there has been increasing a demand for enhancing the feed speed of the single shaft type table feed device of this kind.
By the way, in the table feed device using a feed screw shaft, if the number of working rotations of the feed screw shaft approaches the natural frequency of the feed screw shaft, then it becomes a so called critical speed, thereby producing resonance. Since the critical speed is in inverse proportion to the square of the support distance of the feed screw shaft, if the support distance is set as short as possible to thereby enhance the natural frequency of the feed screw shaft, then the critical speed of the feed screw shaft can be increased effectively. Therefore, in a feed screw shaft having a long length, generally, as shown in FIG. 7, an intermediate support 2 in sliding engagement with the feed screw shaft 1 is set at an intermediate position in the support distance of the feed screw shaft on a base member. In this case, in order to prevent interference between the intermediate support 2 and a nut 4 which is in threadedly engagement with the feed screw shaft 1 and is mounted on a table 3, there is provided a limit switch 5; that is, when the table 3 passes, the intermediate support 2 can be retreated in accordance with the limit switch 5.
Also, in the Japanese Patent No. 2526816, there is disclosed another example of the intermediate support. In this intermediate support, as shown in FIG. 8, two guide rails 7 are fixed to two side portions of a base member in parallel to each other, a pair of table linear motion bearings (that is, table sliders) 8 are fitted on each of the two guide rails 7 in such a manner that they can be freely moved in the axial direction of the guide rails, and a table 3 is fixed to each of the table sliders 8 on the top surfaces thereof. A feed screw shaft 1 is interposed between and extended in parallel to the two guide rails; in particular, one end side of the feed screw shaft 1, which is to be connected with a drive motor 13, is supported by a support unit 11, whereas the opposite end side thereof is supported by a support bearing 12. An intermediate support 14 is interposed between the support bearing 12 and a table nut 4 which is threadedly engaged with the feed screw shaft 1 through balls. Also, the intermediate support 14 includes an intermediate support frame 16 which is supported by intermediate support linear motion bearings (that is, intermediate support sliders) 15, 15 respectively fitted with the guide rails 7, 7, and an intermediate support nut 17 which is threadedly engaged with the feed screw shaft 1 through balls and is supported in such a manner that it is prevented from moving in the axial direction with respect to the intermediate support frame 16 but can be rotated freely. On the other hand, between the feed screw shaft 1 and one guide rail 7, there is disposed an auxiliary feed screw device 20 which comprises an auxiliary feed screw 18 having an axis parallel to the feed screw shaft 1 and supported on the base member, and an intermediate support feed nut 19 which is threadedly engaged with the present auxiliary feed screw 18. And, the intermediate support feed nut 19 is fixed to and mounted on the intermediate support frame 16 of the intermediate support 14. Also, the end portion of the auxiliary feed screw 18 having a uniform pitch and the end portion of the feed screw shafts 1 are connected together by auxiliary feed screw drive means 21 which comprise a timing belt and a timing pulley in such a manner that the auxiliary feed screw 18 can be rotated at one half of the number of rotations of the feed screw shaft 1. With use of the intermediate support 14, if the feed screw shaft 1 is driven or rotated by the drive motor 13, then the table nut 4 is moved and, in linking with the movement of the table nut 4, the intermediate support 14 is moved in the same direction by an amount of one half of the moving amount of the table nut 4. Due to this, the intermediate support 14 is always allowed to support the feed screw shaft 1 almost centrally between the table nut 4 and support bearing 12, thereby being able to enhance the critical speed of the feed screw shaft 1.
Conventionally, a single shaft type table feed device including an auxiliary movable body increases a span between the nut portion of the movable body and the supporting shaft, because the auxiliary movable body having an unloaded hole which is not engaged with the feed screw shaft is interposed between a movable body including a nut portion to be threadedly engaged with a feed screw shaft and a bearing for supporting the end portion of the feed screw shaft.
As a result, the natural frequency of the feed screw shaft is lowered, that is, the critical speed is lowered, thereby often raising a problem that the use of the single shaft type table feed device at the high speed feed is limited. As a measure to deal with this problem, there can be provided an intermediate support in the single shaft type table feed device.
However, in the conventional intermediate support 2 shown in FIG. 7, there is found a drawback as follows: that is, it is necessary to provide a retreat mechanism which is capable of retreating the intermediate support 2 when the table 3 or table nut 4 passes through the intermediate support 2. In fact, the retreat mechanism is complicated in structure and, therefore, it is not proper from viewpoints of not only cost but also space to use the conventional intermediate support 2 including such complicated retreat mechanism as an intermediate support of a single shaft type table feed device inherently having a compact structure.
On the other hand, in the conventional intermediate support 14 shown in FIG. 8 as well, there is also found a drawback as follows: that is, it is necessary to provide the auxiliary feed screw device 20 which is capable of moving the intermediate support 14 in linking with the table nut 4, but the auxiliary feed screw device 20 is complicated in structure. Therefore, similarly to the intermediate support 2, it is not proper to use the conventional intermediate support 14 as an intermediate support of a compact single shaft type table feed device from viewpoints of cost and space.